Does yours have the felt cushion riveted to the back of the receiver? May want to think about getting that replaced before you start dumping parts into your receiver.
Here is a huge parts lot on ebay!! Vintage Remington Model 11 12ga Misc Parts Large Lot | eBay
The screw kits can come from Midwest gun works if they aren't in that lot. Browning Auto 5 Screw Kit, 12 Gauge: MGW spendy, but they are there!
Same with the springs and friction pieces. The foreend-do you have the one that is supposed to go on the gun? I know someone who can fix it if it is cracked. He did an incredible job on mine!